Fix HOSTLIBS on Haiku

Haiku does not have a separate libm, so do not try to link to it.
Signed-off-by: François Revol <revol@free.fr>
Signed-off-by: Mans Rullgard <mans@mansr.com>

configure

@@ -2305,6 +2305,7 @@ case $target_os in
     haiku)
         prefix_default="/boot/common"
         network_extralibs="-lnetwork"
+        host_libs=
         ;;
     sunos)
         FFSERVERLDFLAGS=""